| 摘要: |
| 四川盆地是我国灰霾和大气污染易发和频发区之一，目前关于本地区黑碳气溶胶（black carbon，BC）的相关研究较少。利用2017年11月—2018年12月成都西南城郊地区黑碳气溶胶以及PM2.5观测资料，结合气象资料和其他污染物浓度资料，分析BC和PM2.5浓度，BC浓度在PM2.5浓度中所占比例（黑碳占比）的季节、月、日变化特征及其影响因子。结果表明：（1）BC逐小时浓度范围为0.18—40.51 μg∙m−3，平均值为(5.26±4.68) μg∙m−3，本底浓度为3.34 μg∙m−3。PM2.5逐小时浓度范围为1.00—344.50 μg∙m−3，平均值为(60.02±46.91) μg∙m−3，本底浓度为33.38 μg∙m−3。日变化均呈“白天低，早晨、夜间高”的变化特征，其中冬季浓度最高，春、秋季次之，夏季浓度最低。（2）黑碳占比均值为9.16%±5.13%，白天黑碳占比低，夜间黑碳占比高，且夏季最高，冬季最低。随着空气污染加重，冬季占比缓慢增加，其他三季占比减小。（3）BC与NO2和CO相关性较好，表明西南城郊BC排放主要受机动车尾气、生物质燃烧影响。BC和SO2相关系数偏小，燃煤等工业源排放对西南城郊BC的贡献较小。（4）风速、温度和湿度与BC浓度均有很好的相关性，其中风速对BC浓度的影响最大，当风速小于2.0 m∙s−1时，BC浓度值明显偏高；BC浓度大于20.00 μg∙m−3的高值区主要集中在西北、西南以及东北风向上，即：偏东北方向市中心大气中的污染物，以及西南方向远郊地区的污染物可能对西南城郊高浓度黑碳的贡献更大。 |
| 关键词: 黑碳 黑碳占比 细粒子 变化特征 气象因子 |
| DOI：10.7515/JEE192056 |
| CSTR： |
| 分类号: |
| 基金项目:国家重点研发计划（2016YFA0602004，2018YFC0214002）；四川省科技计划（2018JY0011，2018SZDZX0023）；国家自然科学基金（91644226） |
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| Characteristics of black carbon and PM2.5 concentration and influencing factors over suburban of southwest Chengdu |
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YANG Miaolin, ZHANG Xiaoling, YUAN Liang
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1. Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, College of Atmospheric Science, Chengdu University of Information Technology, Chengdu 610225, China
2. Environmental Meteorology Forecast Center of Beijing-Tianjin-Hebei, Beijing 10089, China
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| Abstract: |
| Background, aim, and scope Black carbon (BC) is an aerosol component produced by the incomplete combustion of fossil fuels and biomass. As a component of PM2.5, it has been associated with air quality, climate change and human health. Due to its twofold effects on air quality and climate change, BC is of wide concern in the atmospheric sciences. Sichuan Basin is experiencing severe air pollution during wintertime in recent years, while limited studies focusing on the BC aerosols in this region. The objective of this study is to reveal the basic feature, main sources of BC and influencing factors, to provide a reliable knowledge for air pollution and BC control. Materials and methods Black carbon was measured at Chengdu suburban site from November 2017 to December 2018 using a seven-channel Aethalometer (AE-33). Only BC concentration with 880 nm wavelength was employed in this study. PM2.5, SO2, NO, CO2 and ground-based meteorological data were derived from Shuangliu weather station in Chengdu. In this study, seasonal, monthly, and diurnal changes of BC and PM2.5 mass concentrations, the ratio of BC in PM2.5 were analyzed over suburban of southwest Chengdu. The relationship between BC and gaseous pollutants and the influences of meteorological conditions on BC concentrations were analyzed. Results BC concentration ranged from 0.18 μg·m−3 to 40.51 μg·m−3, with an average of (5.26±4.68) μg·m−3. PM2.5 concentration ranged from 1.00 μgm−3 to 344.50 μg·m−3, with an average of (60.02±46.91) μg·m−3. The background concentrations of BC and PM2.5 were 3.34 μg·m−3 and 33.38 μg·m−3 respectively. The average ratio of BC in PM2.5 was 9.16%±5.13%. Both the concentrations and the ratio of BC in PM2.5 presented clear diurnal variations, characterized by bimodal types. Two peaks appeared at 07∶00—09∶00 in the morning and 22∶00—23∶00 in the evening, and the lowest value was 15∶00—17∶00 in the afternoon. When PM2.5 concentrations increased, the ratio of BC in PM2.5 decreased. The BC and PM2.5 concentrations were highest in winter and lowest in summer, while the ratio of BC in PM2.5 varied in the opposite trend. Gaseous pollutants CO and NO2 had the strongest correlation with BC, while the correlation coefficient between BC and SO2 was lower. The BC concentration generally higher when the wind speed lower than 2.0 m·s−1. High BC concentration (＞20.00 μg·m−3) mainly occurred in NE, SW and NE winds. Discussion In this study, we only used one site data observed one year in suburban of southwest Chengdu to investigate and discuss the characteristics of BC, PM2.5 and their relationship as well as influencing factors. Based on statistical analysis on BC and gaseous pollutants concentrations, we identified the important contributions of the biomass burning and motor vehicle exhaust to BC emission of this region. In this study, when the PM2.5 concentrations increased, the ratio of BC in PM2.5 decreased. Compared with other research results, the characteristics of the ratio of BC in PM2.5 is different owing to the differences in the meteorological factors and sources of BC in various regions. Conclusions The temporal and spatial characteristics of BC over suburban of southwest Chengdu were influenced by the local source emissions and meteorological conditions. Pollutants from downtown area in the NW direction and outer suburbs in in the SW direction contribute more to the BC concentration. Recommendations and perspectives This study explored the influencing factors of BC concentration level, revealed the air quality situation in Chengdu suburban, which provides some reference for the government to make scientific policy to prevent and control the air pollution in Chengdu. |
| Key words: black carbon the ratio of BC in PM2.5 fine particles characteristics meteorological factors |
